The present invention generally relates to an article and process for coating substrates. More specifically, the invention relates to a non-planar article having a plasma deposited abrasion resistant coating and process for plasma coating non-planar plastic substrates.
A variety of techniques exist for coating substrates with functional coatings. Traditionally chemical vapor deposition (CVD), and physical vapor deposition techniques such as sputtering and evaporation, have been used. These techniques, however, require high deposition temperatures, which limit the substrates that can be coated, and further involve very slow deposition rates. More recently, plasma enhanced chemical vapor deposition (PECVD) processes have been developed to overcome some of these limitations. PECVD can be used to deposit materials on plastic substrates such as polycarbonates, at temperatures lower than the glass transition temperature of the plastic, which was generally not feasible with CVD. In PECVD, the applied electric field enhances the formation of the ionized species, providing a much higher percentage of ionized species that permits the use of low deposition temperatures, e.g. as low as room temperature. However, PECVD still does not generally provide a deposition rate that is high enough to be commercially viable for many applications involving polycarbonates coated with UV absorbing and abrasion resistant layers. In addition, PECVD has not been demonstrated on large complex shapes, but rather has been restricted to planar substrates or non-planar substrates with mild curvature such as ophthalmic lenses.
In attempts to produce coatings with uniform properties on plastic non-planar substrates, some systems move the plasma source relative to the substrate and/or change the process parameters as the substrate translates past the plasma source. While these processes have been shown to produce coating of uniform thickness, they do not provide coatings of uniform abrasion resistance and adhesion. These processes also suffer from being cumbersome, expensive, and require different process parameters for each part design. It is also critical for many applications such as automotive windows where the coated substrate is exposed to outdoor weathering that the coating maintains uniform abrasion resistance upon long-term exposure to UV radiation. It appears, however, that many plasma deposited organosilicon coatings degrade upon exposure to UV resulting in poor abrasion resistance.